1. Field of the Invention
This invention relates generally to the use of seismic sensors in geophysical exploration and more particularly to an apparatus for stabilizing a seismic sensor used in a marine environment.
2. Description of the Related Art
In geophysical exploration, an acoustic signal is generated by a seismic source into the earth. The signal propagates through the earth in the form of a wave front which encounters structural changes in the earth. Part of the wavefront is reflected back to the earth's surface and detected by acoustic sensors such as geophones. The data is relayed from the geophones to seismic processing systems to obtain geophysical information about the substrata.
Geophones can be used on land, in shallow water and in marsh land and normally are magnetic-type geophones containing a magnet and a coil. Either the magnet or the coil is attached to the geophone housing and the other element is freely suspended from the housing. Relative motion between the coil and the magnet produces an electromotive force which produces an electrical signal that is proportional to the velocity of the motion.
When a geophone is used in a marine environment, it often is housed in a cylinder and is either trunnion or gimbal-mounted to maintain a vertical or near-vertical orientation when deployed as required for optimal results. Geophones are very sensitive to mechanical vibrations or motion and generate an unacceptable level of noise when moved by flowing water or the turbulence associated with that flow. Current geophones frequently become unstable when subjected to currents such as those caused by marine tidal action.
The present invention addresses the above-noted problem and provides apparatus for stabilizing geophones in a marine environment which reduces the noise problems created by marine tidal action.